xcode Swift：通过 NSNotificationCenter 的键盘观察器不起作用
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Swift: Keyboard Observer via NSNotificationCenter doesn't work
提问by stoeffn
I'm trying to implement a simple keyboard observer in my iOS 8 Swift app but it really doesn't work. This is the code im currently using:
我正在尝试在我的 iOS 8 Swift 应用程序中实现一个简单的键盘观察器，但它确实不起作用。这是我目前使用的代码：
override func viewDidAppear(animated: Bool) {
NSNotificationCenter().addObserver(self, selector: Selector(keyboardWillAppear()), name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter().addObserver(self, selector: Selector(keyboardWillHide()), name: UIKeyboardWillHideNotification, object: nil)
}
override func viewDidDisappear(animated: Bool) {
NSNotificationCenter().removeObserver(self)
}
func keyboardWillAppear() {
logoHeightConstraint.constant = 128.0
}
func keyboardWillHide() {
logoHeightConstraint.constant = 256.0
}
Strangely both functions to react to the keyboard are called once after starting the app. Nothing happens when I enter or leave a textfield. What am I doing wrong? And by the way: Is altering a constraint the best solution for changing the size of an image?
奇怪的是，在启动应用程序后，对键盘做出反应的两个函数都会被调用一次。当我进入或离开文本字段时没有任何反应。我究竟做错了什么？顺便说一句：改变约束是改变图像大小的最佳解决方案吗？
I really appreciate your help!
我真的很感谢你的帮助！
回答by Patrick Goley
Calling NSNotificationCenter()is instantiating a new NSNotificationCentereach time you call it. Try using NSNotificationCenter.defaultCenter()instead.
每次调用时调用NSNotificationCenter()都会实例化一个新的NSNotificationCenter。尝试使用NSNotificationCenter.defaultCenter()。
回答by JSA986
//keyboard observers
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillAppear"), name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide"), name: UIKeyboardWillHideNotification, object: nil)
func keyboardWillAppear() {
println("Keyboard appeared")
}
func keyboardWillHide() {
println("Keyboard hidden")
}
回答by schirrmacher
Swift 4.0, closures :
Swift 4.0，闭包：
NotificationCenter.default.addObserver(forName: .UIKeyboardDidShow, object: nil, queue: nil, using: { notification in
// do stuff
})
回答by Werner Kratochwil
I prefer to use UIKeyboardWillChangeFrameNotification, because you get informed if the size changes, if e.g. when suggestions are hidden/shown
我更喜欢使用 UIKeyboardWillChangeFrameNotification，因为如果大小发生变化，例如当建议被隐藏/显示时，您会得到通知
//keyboard observers
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(keyboardWillChange), name: UIKeyboardWillChangeFrameNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(keyboardWillHide), name: UIKeyboardWillHideNotification, object: nil)
func keyboardWillChange(notification:NSNotification)
{
print("Keyboard size changed")
}
func keyboardWillHide(notification:NSNotification)
{
print("Keyboard hidden")
}
回答by Van
Swift 3 and above code. Added code for getting height for keyboard
Swift 3 及以上代码。添加了获取键盘高度的代码
func addObservers() {
//keyboard observers
NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidAppear(notification:)), name: NSNotification.Name.UIKeyboardDidShow, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(notification:)), name: NSNotification.Name.UIKeyboardDidHide, object: nil)
}
@objc func keyboardDidAppear(notification: NSNotification) {
print("Keyboard appeared")
let keyboardSize:CGSize = (notification.userInfo![UIKeyboardFrameEndUserInfoKey] as! NSValue).cgRectValue.size
print("Keyboard size: \(keyboardSize)")
let height = min(keyboardSize.height, keyboardSize.width)
let width = max(keyboardSize.height, keyboardSize.width)
print(height)
print(width)
}
@objc func keyboardWillHide(notification: NSNotification) {
print("Keyboard hidden")
}
